The present invention generally relates to an automatic distance measuring device of a type utilizing the principle of triangulation and, more particularly, to an electric rangefinder circuit for processing an output signal generated from a light measuring circuit.
There is known an automatic rangefinder for use in a photographic camera, which range finder comprises a light emitter for projecting pulsating light necessary to illuminate a target object located within one of a plurality of zones at different distances away from the camera, a light receiver for detecting the pulsating light reflected from the target object and including photoresponsive elements so arranged as to monitor the respective zones, each of the photoresponsive elements producing an output the magnitude of which varies as a function of the intensity of the pulsating light detected thereby, and means coupled to the light receiver and responsive to a change in magnitude of the output of any one of the photoresponsive elements to provide an automatic focus control signal necessary to actuate a trigger mechanism to bring the objective lens to one of the focal positions which corresponds to the distance from the camera to such one of the zones when the magnitude of the output of one of the photoresponsive elements monitoring such one of the zones has actually varied due to the presence of the target object in such one of the zones.
Examples of the automatic rangefinder of the type referred to above are disclosed in U.S. Pat. No. Re. 27,461 reissued on Aug. 15, 1972, U.S. Pat. No. 3,723,003 patented on Mar. 27, 1973, and Japanese Patent Laid-open Publication No. 49-49625 laid open to public inspection on May 14, 1974.
In a normal case, it is expected that the magnitude of the output of one of photoresponsive elements of the light receiver varies due to the presence of the target object in a corresponding zone. One distance range can be correspondingly determined in response to the light receiver in this normal case to control the focus of the objective lens or to display the distance measuring result. However, if a plurality of photoresponsive elements vary their magnitude of outputs for some reason, e.g., due to a change in ambient light, at the same time, the distance determination will be confused and result in a failure in controlling the focus or displaying the distance information. This confusion is particularly noticible when at least a pair of photoresponsive elements, which monitor at least a pair of non-neighboring zones, vary the magnitude of their outputs.